1. Field of the Invention
The present invention is in the field of equipment which operates by means of closing a downhole port by pumping a plug, ball, or other device downhole with the drilling fluid, cement, or other fluid.
2. Background Art
It is well known in the art of oil and gas well drilling to operate or actuate downhole equipment by pumping a plug, ball, or other device downhole with the drilling fluid, cement, or other fluid. The term pumpdown plug, pumpable plug, or other such term, as used herein, is intended to include all such devices, whether plugs, balls, or other items.
When it is desired to actuate a piece of downhole equipment, such as a cementing valve, it is common to pump a plug downhole to close off, and sometimes seal, a port through which fluid is being circulated. The closing of this port can then be used to create an increased fluid pressure above the port, to actuate the device. After actuating the downhole equipment in this manner, it is sometimes desired to release the pumpable plug from the port and restore circulation through, the port. When a pumpable plug is released in this manner, it typically proceeds farther downhole. Unless such a released plug is properly captured and retained, it can interfere with, or even prevent, subsequent operations in the well bore below the location from which the plug was released.
It is known to capture such a released plug in a perforated tube below the downhole equipment which the plug was originally used to actuate. Capturing the released plug in a perforated tube has the advantage of allowing fluid flow through the perforations and to the well bore below the capture point. However, a perforated tube will not allow the performance of some subsequent operations which may be desirable, below the capture point, such as wireline operations. Further, if it is necessary to pass other equipment through the plug capture point in the well bore, such as for the purpose of undertaking remedial operations deeper in the well bore, the presence of the captured plug in the perforated tube will prevent such operations. In these situations, if the perforated tube is present, it would have to be removed before passing any equipment beyond the plug capture point.
It is desirable, therefore, to have a method and apparatus for capturing a pumpable plug which has been released, and for allowing the passage of fluid and equipment beyond the plug capture tool to a deeper location in the well bore.